If I renew SSL certificate 30 days before it expires, will I lose the time remaining on it?
In order not to lose remaining time for a Certificate that is close to the expiration date, you need to make sure to purchase a renewal certificate and generate a new CSR. We strongly recommend not to use the original CSR code used during initial certificate activation. Please make sure to purchase and activate a renewal certificate and not a new one - this will also help you deal with validation process in case you have an OV/EV certificate.
NOTE: renewal does not happen automatically, you need to generate a “renewal CSR” code plus a RSA Key, follow up the process similar to activation and then reinstall the Certificate on the server for the renewal to take effect.
Step-by-step renewal instructions are provided in the article: How to renew SSL certificate?